The present invention relates to a hip prosthesis and, in particular, to a ball-type prosthesis having a head stem base that mounts in a femoral recess and supports a ball head, which stem base is secured to the femur with a strap and a femoral neck that interlocks with the head stem base.
A variety of prostheses have been developed to repair and alleviate degenerating hip joints. Efforts have been extended to developing artificial sockets for attachment to the hip and interlocking artificial ball heads for the femur. The day-to-day stresses placed on the prosthesis and joint members present a variety of collective concerns and considerations that must be addressed to facilitate prosthetic installation and achieve long lasting integrity.
Several ball joint, hip replacement systems are disclosed in the patent literature. U.S. Pat. No. 3,765,034 discloses a prosthesis having a tapered spindle that mounts in the femur. An external drill guide plate separately aligns a series of screws to the spindle. U.S. Pat. No. 4,101,985 patent discloses a washer plate and through which a bolt is fitted and mounts to a ball head.
Several systems shown at U.S. Pat. Nos. 5,007,935; 5,376,125; 5,658,339; and 5,810,821 provide plates that fasten with screws to the shank of the femur. Bored sleeve or barrel pieces project from the fastener plates and support concentric fasteners that fasten to a ball head and draw the head to the femur.
U.S. Pat. No. 5,800,553 patent provides a screw fastened external plate with a series of end couplers that collectively extend to a ball head. The couplers include internal and external threads.
The present invention was developed to provide an improved hip prosthesis that optimally distributes the stress and loading to extend implant life. The assembly includes a thrust or strap plate that mounts to the femur with a number of screws mounted to elongated, laterally displaced holes. Stress relieving features are included at the plate. A bored, femoral neck or stein piece transversely extends from the plate (e.g. at an obtuse or oblique angle) and interlocks in non-rotational engagement with a tapered, ball head stem base. A shouldered bolt draws the femoral neck to interlock with the bore of the ball head base as a flanged force plate is drawn into abutment with the femur, whereby the ball head base is secured in a surgically prepared femoral recess. The pieces are constructed from or coated with a material that exhibits a suitable surface porosity, sintering or other abrading material, for example a cobalt-chromium alloy (CrCo) having a yield strength in the range of 35 ksi to 230 ksi, stainless steel, titanium or other biocompatible material.